1. Field of the Invention
The present invention relates to a fuel supply device for an internal combustion engine, and more particularly to a fuel supply device for an internal combustion engine, which performs a fail-safe control for ensuring the restarting of the engine immediately after the engine is stopped with the pressure in the fuel rail being abnormally high.
2. Description of the Related Art
As disclosed, for example, in JP 11-125140 A, in a conventional fuel supply device, an injector is provided in the combustion chamber of each cylinder 27 of the engine, and while the injector is open, fuel in a fuel rail (common rail), which is a high pressure accumulation piping, is injected into the combustion chamber. A high pressure fuel pump is controlled by an electronic control unit so as to maintain the fuel sucked in from a fuel tank at a predetermined high pressure.
In the conventional fuel supply device, however, when the pressure in the fuel rail rises to an excessive degree due to malfunction of the high pressure fuel pump, etc., and the engine at rest, the maximum pressure allowing driving of the injector may be below the pressure in the fuel rail. Thus, when restarting of the engine is attempted immediately thereafter, it can happen that the injector is not driven and the engine cannot be started.
This will be illustrated in detail. When the pressure in the above-mentioned fuel rail rises to an excessive degree, the pressure control valve is opened, and fuel in the fuel rail flows to the low pressure side, whereby the pressure rise in the fuel rail is restricted. Thus, the pressure in the fuel rail is substantially equal to the opening pressure for the pressure control valve for a while. In order to cause fuel in the fuel rail to flow to the low pressure side, the opening pressure for the pressure control valve is normally set to be higher than the maximum pressure allowing driving of the injector. Thus, the pressure in the fuel rail is higher than the maximum pressure allowing driving of the injector for a while.
When an attempt is made to immediately restart the engine under this condition, large current flows through the starter and the battery voltage is reduced, resulting in a marked reduction in the maximum pressure allowing driving of the injector. The injector is a solenoid type electromagnetic valve, and the requisite drive energy for driving the injector is obtained by converting the electrical energy from the power source device of a vehicle-mounted battery, a vehicle-mounted generator, or the like to the magnetic energy. Thus, when the voltage of the battery is reduced, the drive energy is reduced accordingly, with the result that there is a fear of the maximum pressure allowing driving of the injector becoming lower than the pressure in the fuel rail.
Normally, the injector is designed so as to be driven at a pressure somewhat higher than the maximum pressure allowing driving thereof. However, when the pressure in the fuel rail rises to an excessive degree, the pressure control valve provided in the fuel rail is opened, and the fuel in the fuel rail flows to the low pressure side, with the result that the pressure in the fuel rail is a high pressure substantially equal to the opening pressure for the pressure control valve for a while. When the engine is restarted by the starter immediately thereafter, the maximum pressure allowing driving of the injector is reduced due to the reduction in the battery voltage, and there is a fear of this maximum pressure becoming lower than the pressure in the fuel rail and the injector not being driven, making it impossible for the engine to start.
Apart from the above-mentioned case in which the battery voltage is reduced, this also applies to a case in which the battery suffers deterioration, a case in which the pressure in the fuel rail rises to an excessive degree, etc.